Research Question and Background

For many, toothbrushing is a simple, everyday task, but for those with bulbar

dysfunction, this seemingly simple task can become a burden. Amyotrophic lateral sclerosis (ALS), a disease characterized by the progressive degeneration of the motor neurons, affects over 450,000 people worldwide. As ALS progresses, the brain loses the ability to control muscle movement and many people can lose the ability to speak, eat, move, and breathe [1,2]. Some people with ALS can lose function of the muscles in the bulbar area around the mouth and throat, which creates the risk of choking on saliva or other liquids. Due to this increased risk, some resort to ineffective toothbrushing methods or stop brushing their teeth altogether. This is problematic as it can lead to poor oral hygiene which increases the risk of aspirating foreign material into the lungs. As a result, the risk of respiratory infections, a leading cause of death for people with ALS, is increased [3]. Presented with this problem by the Duke ALS Clinic, our design team created SipClip, a suction attachment solution for electric toothbrushes to allow the user to brush their teeth and suction liquid simultaneously.

The goal of our design project is to develop a universal suction attachment for electric toothbrushes to improve the oral hygiene of people with bulbar dysfunction due to ALS and other neurological conditions. Attaching the SipClip to a toothbrush would replace current methods of brushing teeth, which include using a cloth to swab teeth, a dental suction tip to aspirate waste, or not brushing teeth at all. Through multiple prototype iterations and structural and clinical testing, we have developed a device to make brushing one’s teeth a more accessible and independent task for those with ALS, thus increasing oral hygiene and decreasing the risk of choking and respiratory infections.

Methods and Approach

We followed an iterative engineering design process in the creation of our device,

incorporating feedback from users and data from testing in each prototype iteration. We initially determined design constraints and objectives to guide our brainstorming and prototyping processes. Design constraints included suctioning ability and safety. Specifically, that our device not impede the suction of an aspirator and that the material for our device is safe for use by humans in the mouth. Design objectives ordered from most to least important with target values included: ease of use—success based on user feedback; size—less than 48.8 mm (average width of an adult mouth); durability—device lifetime of at least 1 month; weight—less than 285 grams; reproducibility—success based on a user-defined scale; and cost—less than $25 per unit [4].

We developed over 50 ideas during our brainstorming process that integrated three design blocks for our device: a suction head, an interface between the aspirator and head attachment, and a suction control mechanism. By scoring our ideas based on our design criteria, we narrowed our ideas down to an overall design to begin prototyping. We decided to focus on two design blocks, the suction head and aspirator adapter, and determined we would take the idea of a suction collar with a 3D printed tube adapter into prototyping.

Our first design iteration (Figure 1A) included a suction collar that fit around the toothbrush head and a tapered tube adapter to fit the size of standard aspirator tubing. This design posed problems such as how the device would be attached to the toothbrush. To minimize the number of parts on our device, we eliminated designs that required use of external clipping mechanisms and instead focused on creating a design that snapped onto the toothbrush head.

Moving onto our second design iteration (Figure 1B), we met with a design team at Duke’s Innovation Co-Lab to develop ideas to create a new design. From this meeting, we decided to 3D scan toothbrush heads and subtract the dimensions of the scan from a preliminary 3D modeled base design (Figure 2A and 2B). This would allow our device to snap onto the toothbrush head, thus eliminating the need for additional clips. Currently, we have devices compatible with Oral-B Pro 5000 toothbrush heads, but we plan to develop suction head attachments for the three most widely used electric toothbrush brands. Our second design iteration maintained the idea of a suction collar with tubes on either side of the toothbrush head, a tapered tube adapter, and a thin back to reduce bulkiness in the mouth (Figures 1B and 2A). This idea seemed strong in principle, but testing showed that it was unable to suction water successfully. We believe this was due to the suction holes and tubing being too small.

The difficulty suctioning water prompted a new design (Figure 1C). This design is similar to our second iteration, however, two prongs extend in front of the toothbrush bristles (Figure 2B) and the tubing down the sides is of a larger diameter. After testing with team members and professors and determining that our design meets all our design objectives, we printed this design, sterilized the parts, and brought them to the Duke ALS Clinic for initial testing with three people with ALS. Feedback we received from these initial tests prompted the design changes seen in Figure 1D. These changes included: adding ridges to the tapered tube adapter to allow it to stay connected to aspirator tubing and be compatible with tubes of different radius sizes; and thickening the back of the device to reduce the possibility of breaking during initial attachment. Because we originally scanned an Oral-B Pro 500 head but were testing with generic store-bought heads, we had to scale up our CAD model by 3% to account for the slight differences in toothbrush head diameter.

Our initial prototypes were printed using polylactic acid (PLA) plastic filament on Ultimaker 3D printers (Figure 3); however, PLA is not biocompatible for use in a person’s mouth. To account for this, we printed final prototypes for testing using Formlabs’ Dental SG Resin and stereolithography (SLA) printers. This material and printer allow us to print biocompatible designs at a higher resolution than the Ultimaker printer, ensuring that the design has a smooth surface finish while reducing possible growth of bacteria in between printed layers.

We are looking into alternative methods of producing the SipClip as 3D printing is very useful for prototyping, but is inefficient when manufacturing parts in bulk. A current alternative includes injection molding as this would allow us to produce a large number of parts in a material that is biocompatible and slightly more flexible than Dental SG Resin. This will increase durability and decrease long-term production costs.

Description of Final Design

Our final prototype involves a suction collar design with tubes on either side of the toothbrush head. The head of the SipClip, as seen at Point 1 of the labelled CAD model (Figure 4A), features two curved tubes with diameters of 6.2 mm. The tubes run down the sides of the curved shaft of the SipClip (Point 2), which is 43.6 mm in length (Figure 4A). The back of the attachment is thin to avoid making it feel bulky when used. The tubes then converge into a tapered, ridged base (Point 3) with a diameter of 7.5 mm (Figure 4A). The tapered base with ridges allows the attachment to stay firmly connected to multiple sizes of suction tubing. Using Dental SG Resin makes the SipClip strong and hard enough to snap onto the toothbrush head without breaking, but is also light enough at 3 grams to make the part easy to handle. The overall design of the SipClip minimizes size by staying tight on the toothbrush head and minimizes intrusiveness with its thin shape.

To set up the device (Figure 4B), the user first snaps the shaft of the SipClip onto the back of the head of the electric toothbrush. The user then pushes the ridged base of the SipClip inside the end of the aspirator tubing and places the toothbrush head back onto the base of the electric toothbrush. The user can simply switch on the aspirator and toothbrush and begin brushing as usual. Through this mechanism, the user is able to brush their teeth while simultaneously suctioning out waste at a rate that is gentle as to not disturb the cleaning process. Fluid travels from the user’s mouth through the aspirator tubing and into the waste canister of the aspirator.

Preliminary Testing Outcomes

Table 1: Results for Durability Snap Test. Due to using the generic toothbrush head instead of the Oral-B brand head, we tested 2% and 3% size increases.

	Total snaps withstood	Location of break (# of snap)
2% size increase	121	Back of device (10)
2% size increase	300 with no breaks	Bottom edge (25)
3% size increase	300 with no breaks	Bottom edge (10)
3% size increase	300 with no breaks	Bottom edge (4)
(modified) 3% size increase	300 with no breaks	NA

We have begun preliminary testing to assess our device’s performance in durability, safety, and ease of use. Durability of the device is important as it is directly related to the general safety of the device. A snap test was conducted which involved snapping the device on and off a toothbrush head—simulating everyday use of the part—to determine the maximum number of snaps the device could withstand before breaking. Our target durability was 120 snaps, or an estimated use of one month. Results from the snap test (Table 1) provided the maximum lifetime of the device along with physical evidence of the location of breaks so the design could be revised accordingly. Our durability testing showed that the bottom corners of our device, visible in Figure 1C, kept snapping off, so we addressed this by filleting the edges to reduce their protuberance. Additionalsafetyresearch,suchasteststodeterminethebestmethodforcleaning the device, will be conducted through bacterial testing and consultations with experts with experience in oral devices, including dentists and biomedical engineers, and interactions with people familiar with ALS, such as occupational therapists.

Clinical testing for ease of use with Duke IRB approval is currently in progress. This will take place at the Duke ALS Clinic and will involve individuals selected on the basis that they have bulbar dysfunction and have given consent. Three to five individuals will be provided a demonstration of the set-up of the device and will use the device over the course of a week. Users are consented and their feedback will be collected through a Qualtrics survey which is used to evaluate whether the product made toothbrushing easier. The testing is especially important regarding qualities that are more difficult to quantify—ease of use and suctioning ability.

We gave our third design iteration (Figure 1C) to three people with ALS at the Duke ALS Clinic on December 18th. One user who tested the part at the ALS Clinic enjoyed using the part, giving it a “thumbs up”, and took more parts home to use. Some of these users had difficulty with the parts breaking when trying to snap the part onto the toothbrush, which we addressed in our fourth design iteration (Figure 1D) by thickening the back of the part. We gave our fourth design iteration to clients at the ALS Clinic on March 4th and 12th and received positive feedback from initial users regarding suctioning ability and ease of use. Additional users are actively being identified for long-term testing and will be reported on when testing concludes.

Cost

We calculated the standard cost of producing our final prototype with the unit price of the

FormLabs Dental SG Resin and the volume of resin used to print one device. Dental resin is priced at $299 per liter, and it requires roughly 7 mL of resin to print one unit. This makes the unit price of our part, not factoring labor costs, about $2.09.

Significance

Our device has the potential to make the lives of those with ALS and other neurodegenerative diseases more comfortable by making tooth brushing, an essential daily function, more accessible. Successful use of our device would increase the oral hygiene of people with disabilities that limit mobility. This would decrease the unnecessary headaches associated with poor oral hygiene, such as tooth decay and unwanted dentist visits, and help prevent even more serious problems, such as gum disease and respiratory infections.

Our attachment also has potential uses for others who have disabilities that make spitting or swallowing difficult. Diseases which could lead to dysphagia—difficulty swallowing or spitting due to problems with bulbar muscles—include cerebral palsy, muscular dystrophy, Parkinson’s disease, and multiple sclerosis. Furthermore, the device could also greatly benefit older adults who have difficulty swallowing or who are immobile. For example, the device would allow for people to remain seated or in bed, making it much easier for them or their caregiver to efficiently and quickly clean their teeth.

We have reached out to local dentists and assisted living communities in order to get their feedback on our device. Dr. Goldenberg, a pediatric dentist at The Greensboro Center for Pediatric Dentistry, was very enthusiastic about the potential groups who could benefit from our device. While most of his patients would not need our device, he did acknowledge that a few patients with mobility issues could benefit from the SipClip. Other groups he mentioned included older adults, people with spinal injuries, people who are bedridden, or people who are mentally, physically, or developmentally challenged. In addition, we talked with the Directors of Home Care and Rehabilitation at WhiteStone, an assisted living center in Greensboro, who both were positive about the applications of our device to aid older adults, specifically those with Parkinson’s disease. Furthermore, because our device requires a portable suction device, we researched the projected market for such devices and found it is predicted to increase. The aging global population along with the growing market for portable suction devices [5] indicate the market for SipClip may also increase.

Our suction attachment has the potential of making tooth brushing more accessible to anyone who has bulbar dysfunction. The benefits of this device include not only the physical and mental benefits associated with good oral hygiene and an increase in user independence, but also the cost benefits of reduced medical bills due to fewer trips to the dentist and a reduced risk of respiratory infection. With continued development and testing of our device, we hope to expand the reach of our product to better the lives of those affected by bulbar dysfunction and other neurological conditions.